The Collaborative International Dictionary of English v.0.48:

Betty \Bet"ty\, n.
   1. [Supposed to be a cant word, from Betty, for Elizabeth, as
      such an instrument is also called Bess (i. e., Elizabeth)
      in the Canting Dictionary of 1725, and Jenny (i. e.,
      Jane).] A short bar used by thieves to wrench doors open.
      [Written also bettee.]
      [1913 Webster]

            The powerful betty, or the artful picklock.
                                                  --Arbuthnot.
      [1913 Webster]

   2. [Betty, nickname for Elizabeth.] A name of contempt given
      to a man who interferes with the duties of women in a
      household, or who occupies himself with womanish matters.
      [1913 Webster]

   3. A pear-shaped bottle covered round with straw, in which
      olive oil is sometimes brought from Italy; -- called by
      chemists a Florence flask. [U. S.] --Bartlett.
      [1913 Webster]